The present invention relates to an image processing apparatus and more particularly to a memory control means which is suitable to simultaneously display a large picture and small pictures inset in the large picture which are provided by processing an input video signal in a reduction and division manner using a digital technique such as a memory.
Conventionally, there have been proposed systems for simultaneously displaying a plurality of pictures by reducing a picture image through digital processing. This technique has been applied to a magnetic recording/reproducing device. For example, this technique has been implemented for functions such as the viewing a TV broadcasting program while reproducing a video tape on the same display screen, a multi-picture screen (or picture-in-picture screen) in which a plurality of TV broadcasting programs are displayed on a single display screen, etc.
As an example of the conventional systems, the picture-in-picture technique in TV broadcasting reception is disclosed in U.S. Pat. No. 4,249,213, issued to Imaide et al on Feb. 3, 1981, and assigned to the assignee of the present invention. The technique disclosed in this reference is to combine two pictures using a memory. More specifically, by setting the period of the memory read shorter than that of the memory write to reduce the image, or controlling the read timings, two asynchronous video signals are aligned in their time base. Thus, a reduced picture, referred to as a small picture, can be inset in a portion of a picture, referred to as a large picture, displayed on the entire screen of a picture tube.
The above proposed technique is to inset one small picture in a large picture. By increasing the number of small pictures to 2, 3, . . . , many pictures can be simultaneously viewed on the same screen. However, only arranging in parallel the systems including tuners in order to increase the number of small pictures gives rise to a remarkable increase in the production cost. Additionally, there is proposed a technique of using a tuner, an A/D converter, etc. as a single system so that they are time-divisionally changed over. This technique, however, provides the problem of fluctuations of small pictures in the vertical direction. This is because one frame of a video signal in the NTSC System is constituted by two fields, i.e., ODD- and EVEN-numbered fields, and mere use of the above time-division change-over may cause vertical shifts of the entire small images owing to a difference of 0.5 H (1/2 of the horizontal scanning period) between the odd- and even-numbered fields.